Rotor for a helicopter



Oct. 15, 1963 B. POSNIAK ETAL ROTOR FOR A HELICOPTER 4 Sheets-Sheet lFiled Dec. l, 1960 BENJAMA/V POS/WAK GEORGE AMCCOUBREV EDWARD BAB/Anz By/Mfn il 01a Oct. 15, 1963 B. PosNlAK ETAL RoToR FOR A HELICOPTER 4Sheets-Sheet 2 Filed Dec. l, 1960 Oct. 15, 1963 B. PosNlAK ETAL RoToRFOR A HELICOPTER 4 Sheets-Sheet 3 Filed Dec. l, 1960 d, H Z M Oct. 15,1963 B, POSNIAK ETAL 3,106,963

ROTQR FOR A HELICOPTER The invention relates to a rotor Afor ahelicopter, and the general object of the invention is to provideimproved means which enable the several blades of the rotor to be foldedso as to reduce the space required for the storage or transportation ofthe helicopter.

`In a rotor embodying the invention, the outer lifting structure of eachblade is pivotally movable about a hinge axis which is outwardly spacedfrom the lead-lag axis and which is normally substantially vertical. Areleasabie device is provided on each blade :for normally holding theouter lifting structure in its extended position, this device whenreleased permitting the lifting structure of the blade to be swung aboutthe hinge axis to a folded position. Preferably, the releasable deviceengages an arm which is fixedly connected with the lifting structure ofthe blade and which extends inwardly beyond the pivotal axis. A rotor asabove set forth is not herein broadly claimed, such a rotor being setIforth and claimed in the copendin-g application of Richard H. Hollrockand Robert B. Bossier, lr., Serial No. 128,711, tiled August 2, 1961,for Rotor lfor a Helicopter.

One of the objects of the present invention is to provide variousimproved features of structure and arrangement for the devices whichreleasably hold the blades in extended positions and to provide variousimproved features of structure and arrangement for the means whichoperate and hold the last said devices.

It may be desirable to fold the several blades of the rotor at differentlevels, and in accordance with the invention each hinge axis isadjustable to different angular positions with respect to a radial planethrough the rotor axis, and means is provided for retaining the partswith the hinge axis in the adjusted position. With the hinge axis of anyone blade at a selected angle, the folding movement of the liftingstructure is effected at a corresponding level.

In accordance ywith usual practice each blade comprises an inboardmember connected with the rotor hub and the lifting structure of theblade and the supporting elements therefor are movable relatively to theinboard member and about a radial axis, this relative rotative movementbeing provided primarly -for pitch changing during rotor rotation. Thiscapability of relative rotative movement is utilized when the rotor isstationary for changing the angle of the hinge axis relatively to saidradial plane preparatory to folding. The before-mentioned retainingmeans serves for holding the parte in their adjusted positions after theangle of said hinge axis has been changed.

A rotor embodying the invention has other novel and advantageousfeatures which will be more fully understood from the drawings and thefollowing description and claims.

The drawings show a preferred embodiment of the invention and suchembodiment will be described, but it will be understood that variouschanges may be made from the construction disclosed, and that thedrawings and description are not to be construed as defining or limitingthe scope of the invention, the claims forming a part of thisspecication being relied upon for that purpose.

Of the drawings:

FIG. 1 is a schematic plan view of a helicopter having a rotor embodyingthe invention.

FIG. 2 is a plan view of the inboard portion of one blade of the rotor,together with a fragment of the hub.

FIG. 3 is a side view of the blade and hub parts shown in FIG. 2.

FIG. 4 is an enlarged plan of a portion of FIG. 2, this view showing theparts to which the invention -more particularly relates.

FIG. 5A is a vertical sectional view taken along the line 5A-5A of FIG.4.

FIG. 5B is an extension of FIG. 5A in the outbomd direction.

FIG. 6 is a vertical section-a1 view taken along the line 6-45 of FIG.4.

FIG. 7 is a view taken in the direction of the arrows 7, 7 in FIG. 4,but showing only the arms that are engaged by the radially movableretaining member.

FIG. 8 is a combined sectional and elevational view taken lalong theline -S-S of FIG. 4, this view showing the radially movable retainingmember but omitting the parts with which the retaining member engages.

FIG. 9 is a plan view of the retaining member and associated parts asshown in FIG. 8.

FIG. 10 is a horizontal sectional view taken along the line liti-1) ofFIG. 8.

FIG. Ill is an enlarged fragmentary sectional View taken lalong the line11-11 of FIG. 6.

FIG. l2 is a view generally similar to FIG. 4, but showing the parts inpositions wherein the folding is permitted and showing the blade partlyfolded.

FIG. 13 is a vertical sectional view taken along the :line 13-13 of FlG.12.

General Organization Referring to the drawings, and more particularlyFIG. 1 thereof, 10 represents the fuselage of a helicopter having arotor which includes mechanisms embodying the invention. The rotor ofthe helicopter comprises a plurality of generally radial blades 14, 14which are connected with a hub 16 and are uniformly spaced about acentral vertical axis. The hub 16 is connected with a vertical mainshaft (not shown) extending upwardly from the fuselage 10. As shown, therotor has four blades, but the invention is not necessarily so limited.

When there are four blades, ias shown, the hub 16 preferably has fourradi-al arms, one of the anms being shown at 1S in FIGS. 2 and 3. Theinboard member -20 of each blade 14 is connected with the correspondinghub arm 18 -for movement about a horizont-al flapping axis at 22 and formovement about a vertical lead-lag axis at 24. For collective andcyclical changes in pitch, the outboard or lifting structure 26 of eachblade is rotatively movable relatively to said inboard Imember 2t) andabout a radial axis. Such rotative movements of the structures 26, 26 ofthe several blades are effected and controlled by means of aerodynamicservo-flaps 2S, 28 carried by the respective lifting structures 216, Z6and adjustable relatively thereto about axes parallel with said radialaxes. Mechanism controlled or actuated by the pilot is provided formoving and controlling the flaps 2S, 28 so as to change and maintain theblade pitches for all conditions of flight.

As shown in FlG. 3 each hub arm 18 is preferably bifurcated and a pivotblock 29 is located between the bifurcations. The block `Z9 has avertical bearing opening therein for a lead-lag pivot pin which providesfor pivotal movement about said axis 24. The inboard blade member 2t)has an outer tubular portion 30 and said member is bifurcated at itsinner end as shown in FIG. 2 to provide bifurcations 32 and 34. Thebifurcations embrace said pivot block 29 to which they are pivotallyconnected for `flapping movements about the axis 22.

The lifting structure 26 of each blade is carried by an inner supportingelement 36 and the inner portion 37 of said inner supporting element istubular and surrounds the tubular portion Si? of the inboard member 2i).Bearings 38 and 46 are interposed between the tubular portions 30 and37, these bearings permitting the outboard portion of the blade to turnrelatively to the inboard member for elfecting changes in pitch.Tension-torsion members 4?., 42 are provided for preventing outwardmovement of the outboard blade portion and for resisting relativerotative movement thereof. The members 42, 42 have their inboard endssuitably connected with the inboard member 20 and they have theiroutboard ends connected with the inner supporting member 36 by means ofbolts 44, 44 in flanges 45, 45.

As shown, the main outboard or lifting structure 26 of each blade 14comprises a radial spar in which is connected with an outer supportingelement 48. The outer supporting element 4S is normally iixedlyconnected with the inner supporting element 36 by means to be fullydescribed. The spar 46 provides the required airfoil shape for theleading edge of the lifting structure 26 and said spar carries aplurality of panels 50 which serve to provide the required airfoil shapefor the trailing portion of the structure. The details of the outboardor lifting structure 26 of the blade may be as set forth in the Lubben,Schauble and McCoubrey application Serial No. 850,953 led November 4,1959 and entitled Helicopter Rotor and Method of Making a Blade MemberThereof.

An azimuth mechanism, not shown, is provided at the lower end of themain shaft which is hollow. Vertical rods, not shown, extend upwardlyfrom the azimuth mechanism and through the shaft, these rodscorresponding in number to the number of blades. The rods are connectedrespectively with levers one of which is shown at 52 in FIGS. 3 and 4,the levers being pivoted to the hub i6. The outboard end of each lever52 is connected with the upper end of a vertical link 54. The lower endof the link 54 is connected with one arm of a bell crank 56 which ispivoted at 58 to the inboard member 20. The other arm of the bell crankis connected by a link 6i) with the leading end of a lever 62 which ispivoted to the member 2i). Said lever 62 is pivoted between its ends at64 and the trailing end of said lever is connected with radial links 66and 63. The outboard end of the link 68 is connected with a lever 70pivoted to a bracket 72 on the spar 46. A radial link 74 is connected atits inboard end to the lever itl and said link '74 extends outwardlywithin the panels Sil. At its outboard end the link 7d is connected tothe flap 28 by suitable means, not shown, this means including a bellcrank and a transverse link.

When any rod within the shaft is moved upwardly by the azimuthmechanism, the corresponding link 52 is moved downwardly, the link 66 ismoved inwardly, and the links 66, 63 and 74 are moved outwardly. Theconnection from the link 74 to the iiap 28 is such that outward movementof the link causes the tlap to move in the negative direction, that is,in the direction for downward movement of its leading edge. Theincreased negative pitch of the iiap tends to move the trailing edge oithe lifting structure 26 downwardly with resultant increased positiveblade pitch. The described motions are reversed when the azimuthmechanism causes downward movement of the rod in the shaft.

The azimuth mechanism is pilot operable and by means of said mechanismand the last above described linkage the pilot can control the angles ofthe aps 28, 2S and can thus control the pitches of the bladescollectively or cyclically or both. While differing in some respects,the

, various parts for controlling the pitches of the blades may beconstructed as more fully disclosed in the Hartswick application SerialNo. 43,830 tiled July 19, 1960 and entitled Rotor Control System for aHelicopter.

Pitch Lock Mechanism A centrifugally controlled means is preferablyprovided i on each blade for locking the outboard portion of the bladeto prevent rotative pitch changing movement relatively to the inboardmember 2t? when the rotor is stationary or is rotating below apredetermined speed. The locked position is sometimes referred to as apredetermined initial position.

Referring more particularly to FIGS. 3, 4, 5A and 6, a ring 76 isconnected to the inboard end of the tubular portion 37 of the innersupporting element 36, this ring being provided with a notch 7S. Themanner of connection of the ring to the tubular portion 37 ishereinafter more fully described, but it is here pointed out that theconnection is such that relative rotation is prevented. The inboardmember 20 is provided with outwardly extending flanges Si?, 8@ betweenwhich there is secured a block 82. The block S2 is bifurcated at itsoutboard end and a locking member 84 is located between the bifurcationsof the block, being movable about a pivot pin S5. At the outboard end ofthe member 84 is a tooth S8 which is adapted to enter the notch 78 inthe ring 76. A compression spring biases the member S41 for entry of thetooth in the notch. The radially inward portion of the member 84 at 92constitutes a weight which during rotor rotation acts centriiugally tomove the tooth 88 out of the notch 78. A pin 94 limits outward movementof the weight portion 92. Preferably, the connection for the ring 76includes resilient cushion elements 96, 96 as shown in FIG. 5A. Thecushion members 96, 96 are formed of rubber or equivalent material.

When the rotor is stationary or rotating at less than said predeterminedspeed, the spring 9@ holds the member 84 with the tooth titi in thenotch 78, thus holding the outboard or lifting portion of the blade inits said predetermined initial position. When the rotor is rotated at aspeed above said predetermined speed, the weight 92 acts centrifugallyin opposition to said spring 90 to move the tooth SS out of the notch 73so that the outer lifting portion 26 of the blade is free to turn underthe control of the ap 28.

When the rotor speedA is decreasing and falls below said predeterminedspeed, each lifting portion 26 tends to turn to its said initialposition. When the blade portion reaches said position, the tooth S8snaps into the notch 7S. The cushion elements 95, 96 permit slightrotative movement of the ring 76 relatively to the member 28 and theythus absorb shock.

Folding and Retaining Mechanism The outer supporting element 4S isconnected with the inner supporting element 36 for pivotal movementabout a hinge axis perpendicular to the radial axis of ythe blade. Forconvenience of description this axis will be referred to as vertical,but during flight it is inclined in a radial plane through the rotoraxis iu accordance with the coning angle of the blade and it may atother times be inclined with respect to said radial plane for a purposeto be hereinafter explained.

As best shown in FIG. 5B, the inner supporting element 35 has a verticalaperture therein near its outer end and a vertical hinge pin 98 isiitted within the aperture, a bushing preferably being interposed. Theouter supporting element 48 preferably has upper and lower bifurcationsMtl and 192 which are apertured to receive the upper and lower portionsof the hinge pin 93, suitable bushings being provided. A collar 164prevents axial movement of the pin. The described hinge joint permitsthe lifting structure 26 of the blade and the outer supponting element48 to be pivotally moved for folding purposes relatively to the innersupporting element 36.

In `order/that folding may be elfected without interfering with theconnection for controlling the ap 28, the

before-mentioned links 66 and 68 are pivotally connected with each otherat 166 for relative movement about a vertical pivotal axis which is atleast approximately in alignment with the hinge axis. As shown, abracket 13S is secured to the member 48, and a transverse link ispivoted at its leading end to said bracket for movement about a verticalaxis. The link 11G at its trailing end is pivotally connected with thelinks 66 and 68 at said axis 166. The link 11G serves to support saidlinks 66 and 68 and to prevent any substantially forward or rearwardshifting of the axis 106. The axis 106 may shift inwardly or outwardlyas the links 66 and 68 are moved to transmit motion to the flap 28, butthe axis 166 is in any event near the hinge axis and hinging or foldingcan be effected without disturbing the connection between the links.Referring particularly to FIG. 3, it will be seen that when folding iseffected in either direction by moving the `outboard portion of theblade clockwise or counterclockwise the bracket 1&8 and the link 68 movein substantial unison and without any interference with each other.

Means are provided for releasably retaining the lifting structure 26 ofthe blade and the outer supporting element 48 in their normal positions,and said means preferably includes an arm such as 112 which is ixedlyconnected with said outer supporting element and extends inwardly `to asubstantial extent beyond the hinge axis. The last said means alsoincludes a relatively movable retaining device, sometimes hereinafterreferred to as the first retaining device, which is engageable with theinner end portion of said ann 112 and is adapted in one position toprevent pivotal folding movement of the outer supporting element 48 andthe lifting structure 26 relatively to the inner supporting element 36which device is adapted in another position to permit such pivotalfolding movement. As shown, said relatively movable first retainingdevice is carried by the inner supporting element 36 as shown at 128 andsaid device is movable relatively to the last said supporting element,preferably rectilinearly, into and `out of engagement with said arm 112.

Preferably there are two similar arms 112 and 114 which are securedrespectively to the upper and lower bifurcations 180 and 102 of theouter supporting element 4S. The arms l112 and `114 are respectivelyabove and below the inner supporting element 36. As shown, the members112 and 114 are apertured at their outer portions to receive and t thehinge pin 98 and they are connected with the bifurcations 160 and 102 bybolts 116 and 118. Each of the arms l112 and 114 at the inner endthereof has two loppositely disposed inclined faces 122, 122 which areexposed toward the hub. Preferably as shown in FIGS. 4, 7, and l2 eachof said arms 112 and 114 is forked at its inner end to provide twotransversely spaced prongs 120, 120. When the prongs 120, 121! areprovided, said faces 122, 122 are on said prongs and said faces facetoward each other and diverge inwardly.

A retaining device 128 is radially movable along a cylindrical portion130 of the inner supporting element 36 and when there are |twosuperposed arms 112 and 114 on the outer supporting element 48 theretaining device has two superposed portions which are engageablerespectively with said superposed arms. Referring particularly to FIGS.4, 5A, 8, 9 :and l0, the retaining device preferably comprises twocompanion parts 132, 1'34 that are similar except for reversal. Theseparts slidably engage the portion 130, and they are engageable with thearms 112 and 1114 and more particularly with the prongs 120, 120 thereofas hereinafter more fully explained.

A manually operable means is provided for moving the retaining device128 in the manner above stated. This means may be widely varied as todetails of construction, but as shown there are two similar partlycylindrical members 136, 138 which surround and engage a cylindricalpart of the tubular portion 37 of the inner supporting element 36. Thesemembers are provided at the top with ilanges 140 and 141 that are atopposite sides of a radially extending operating member 142, saidflanges and said operating member being connected with each other bybolts 144, 144. Similar flanges and a similar operating member areprovided at the bottom but are not fully shown.

The two parts 132, 134 of the retaining device have flanges 146 and 148which are respectively connected by rivets 149 or otherwise withoutwardly projecting narrow portions of the partly cylindrical members136, 138. The two parts 132, 134 of the retaining device areadditionally connected with the members 136, 138 by means of bolts 150,159 at the top and bottom, said bolts extending between said pants 132,134 and said `operating members 142 and 145. Spacers `152, `152 areprovided at the top and at the bottom between the parts 132, 134 and theoperating members.

As best shown in FIG. 8, the parts 132 and 134 are provided near the topwith notches having faces 154, 154 which diverge inwardly to engage andtit the diverging faces 122 on the prongs of the upper arm 112. Saidnotches at their outer ends have opposite beveled faces 156 and 158which diverge outwardly to facilitate entry of the prongs 112, 112 intothe notches. When the retaining device comprising the parts 132 and 134is moved outwardly, the prongs of the arms 112 :and 114 are entered inthe notches in the retaining member, and the diverging surfaces 122, 122and 154, 154 fit each other so .as to prevent any lost motion at theinner ends of the arms and thus prevent any pivotal movement about thehinge axis.

As shown in the drawings, a small clearance is provided between the twoparts 132 and 134 of the retaining device. These parts are held by theoutwardly projecting narrow portions of members 136, 138 and they arealso held by the bolts 150, 'y and the spacers 152, 1-52. These severalholding means for the parts I132 and 134 are flexible within narrowlimits, and said parts are forced toward each other and into iirmengagement with the portion -130 of the supporting element 36 when theinwardly diverging faces 154, 2154 on said members are engaged with theinwardly diverging faces '122, 122 on the prongs 120, 120. The extent ofactual movement of said parts toward each other may be very small, butthe movement avoids any possible lost motion between said parts 132, 134and said portion 138.

The means for radially moving the retaining device 128 also includes amanually operable lever which is connected with the inner supportingelement 36 for moving about an axis perpendicular to said radial axes,together with a generally radial link which is pivotally connected atits respective ends with said lever and with said retaining device 128so that the lever upon pivotal movement serves to move lthe retainingdevice either into or out of engagement with the arm 112, or the arms112 and 114. Th pivotal axis of the lever and the axes of pivotalconnection of the link are so related that an overcenter toggle actionis provided when the lever moves the retaining device into engagementwith the arm.

The before-mentioned lever is preferably a bail 166 which is pivoted tothe tubular portion -37 at 162, a similar pivot l163 being provided atthe opposite end. The bail is connected with the operating member 142 bya link 164, the link being pivoted to the bail at 166 and being pivoted'to the operating member 142 at 168. A similar link l169 is provided atthe opposite side. With the parts in the positions shown in IFIGS. 2, 3,4 and 5A, the retaining device -128 is firmly engaged with the arms L12and :114 to prevent any movement about the hinge or folding axis. Theparts are so proportioned that there is a toggle action when the bail ismoved to the position shown, the pivotal axis 166 being overcenter withrespect to the axes 162 and 168. The links 164 and 169 iare adjustablein length to ensure proper toggle action. During operation, the partsare held in the positions shown partly by the toggle action and partlyby the centrifugal force acting on the bail during rotor rotation.

Means for Holding Hinge Axis at Selected Angle ln accordance with theinvention, the hinge axis for range.

folding is angularly adjustable with respect to a radial plane throughthe rotor axis and an optionally usable means is provided for retainingsaid hinge axis at any one of a plurality of angles with respect to saidradial plane so that folding of the outboard lifting structure may beeffected yat a selected one of a plurality of levels.

The inner supporting member 36 and the parts carried thereby arerotatively movable relatively to the inboard member 2t) and about aradial axis in the conventional manner for pitch changing purposes. Thelast said rotative movement serves to change the angle of the hinge axiswith respect to a radial plane through the rotor axis, but such angularchange is merely incidental and has no significance during normaloperation. However, this capability of angular adjustment of the hingeaxis is preferably utilized obtaining the before-mentioned hinge axisangle that is desirable for folding. When folding is to Vbe effected,the inner supporting member is manually moved to locate the hinge axisat a selected angle. The flap 2S constitutes the effective portion ofthe pitch changing means `and this flap has no pitch changing effectwhen the rotor is idle and when folding is to be effective. The pitchchanging means therefore leaves the inner supporting element 36 and thehinge means free to be rotatively `adjusted relatively to the inboardmember. A manually operable retaining device, sometimes hereinafterreferred to as the second retaining device, is provided for retainingsaid inner suporting member and the hinge device in any one of aplurality of positions to which they may have moved with the result thatfolding of the outboard lifting structures may be effected as abovedescribed. The tooth I38 of the pitch lock mechansm ordinarily holds thehinge axis at a predetermined position `when the rotor is idle, and ifthis is not the desired position for folding said tooth is manuallydisengaged.`

The details of the means or device for retaining the inner supportingmember in a selected position may be widely varied, but the presentlypreferred means is shown in the drawings and will be described. Thebefore-described ring 76 is not mounted directly on the portion 37 butit is so mounted by means of an interposedring 170. The ring 7 6 is soconnected =with the ring l174? that relative rotation is prevented. Thetwo rings are hereinafter sometimes referred to as a ring structure. Theportion 37 of the inner supporting member 36 and the ring 171i areprovided with an annular series of inteimeshing splines or teeth 172which prevent any relative rotation but which permit the ring 17% to bemoved radially inwardly or outwardly. The inboard member Ztl is providedwith an annular series of teeth 174 and the ring 17@ is provided with an`annular series of teeth 176. The teeth 176 are adapted to intermeshwith the teeth 1174 when the ring 17@ is moved radially inwardly to anoperative position. Suitable means, such as a stop i177, is provided forpreventing the ring 17u from moving inwardly beyond the operativeposition wherein there is full interengagement of the teeth 176 and 174.

When the ring 17d is in the inoperative position shown in FIG. 4, theinner supporting element 36 and the parts carried thereby can be turnedto adjust the hinge axis to any one of a plurality of angles within areasonable The pitch lock tooth 88 must have been irst disengaged fromthe ring '76. inasmuch as the element 36 and the parts thereon arenormally moved rotatively only by the ap 2.8, it is obvious that, withthe rotor idle, neither the flap 2S nor its control linkage offers anysubstantial resistance. However, some resistance is offered by thetension-torsion members 42, 42.

-After the turning to locate the hinge axis yat the required angle, thering 17d is moved to its operative position as shown in FIG. 13, and insaid position the ring serves yas a retaining device to prevent anyrelative rotative movement of the inner supporting element 36, and thehinge axis is held at a selected angle. Said ring 170,

when -in its inoperative position, leaves said inner supporting member36 and the parts carried thereby free for conventional rotativemovements under the control of the flap 2S.

A manually operable means is provided for moving the retaining device17@ into and out of its operative position and preferably the handle orYbail i169 is used for this purpose.

The ring 170 is provided with upper and lower bosses 17S and 18d towhich are secured upper and lower tubes 182 and 184 as best shown inFIG. 1l. the upper and lower operating members `142, 145 are rods 156,188 which extend radially inwardly and into the respective tubes 132.,184. Each tube 182, 184 has an inturned ange 190 at its outer end andeach rod 185, 18S has an outwardly projecting annular llange thereonwhich engages the flange 19t) on the tube. These interengaged flangesprevent any inward movement of fthe tubes and of the ring 17d relativelyto the rods beyond the positions that are shown. Springs '194, 196respectively surround the rods 1556, 188, the outer ends of the springsabutting against collars on the rods and the inner ends of the springs`abutting against the ends of the tubes 182, 184. Preferably, but notnecessarily, the ring 171i is provided with a third boss 198 and a thirdtube `2021. Connected between the member 136 and the last said boss andtube is a third rod 264 provided with a third `spring 206.

With the parts in the positions shown in FIGS. 2, 3, 4 and 5A thesprings l194, 196 and Zilli are fully expanded. When folding is to beeffected, the bail 16d is moved inwardly to withdraw the retainingmember 12S so as to release the arms 112 and 114 thus permitting theouter portion of the blade to swing about the hinge axis in eitherdirection. FIG. l2 shows the arms moved out of their normal positions.When the bail 16d is moved as `above stated, the ring 176 is movedinwardly to engage the teeth 174 with the teeth 176 and to thus retain-the element 36 and its attached parts against any relative rotativemovement. The springs 194, 196 and 211i) are compressed and they holdthe ring 17d in its inner position. Preferably, a spring biased latch268 is provided which is pivoted to the portion 37, this latch having ahook which is engageable in a notch in the bail 169 so as to retain thebail in the position corresponding to the releasing or inoperativeposition of Vthe retaining device 12S and corresponding to the operativeposition of the retaining device 170.

It should be particularly observed that the teeth 176 of the secondretaining device engage the teeth 174 before the first retaining device12S is moved suiciently to fully release the arms 112 and 114. Thusthere is no intermediate position wherein the outboard portion of theblade would be free to move about the hinge axis and wherein the innersupporting element 36 would at the same time be free to move about itsradial axis. lf there were such an intermediate position, the outboardportion ofthe blade might be so moved out of ycontrol by a gust of windor otherwise, `and the weight of the angularly positioned outboardportion of 'the blade would then tend to turn the inner supportingelement 36 about its said radial `axis. This turning tendency might besuch that the operator could not effectively resist it. If the innersupporting element 36 were permitted to so turn, the folding axis wouldbe moved out of its intended angular position and folding at theintended level could not be effected.

When the blades are to be folded, it is necessary for the pilot oroperator to decide upon a general plan of folding. In accordance withone plan the blades are turned to approxi-mately diagonal positions. Asshown in FlG. 1, the blade in position A is folded countercloclewise tothe position shown at A in full lines and the blade art position B isalso folded counterclockwise to the position shown at B in full lines.The blade at position C is folded clockwise to the position shown at Cin full lines and the blade at position B is folded clockwise to theposition shown at E in full lines. As shown in FIG. 1, the bladesConnected with A and C are above the blades B and D, but this pattern offolding is not essential.

Referring for example to the blades at the normal positions A and B itwill be seen that the axes for these blades must be at different anglesfor the bla-des to fold into the superposed positions shown by fulllines. It is therefore necessary for the operator before folding each'blade to adjust the angle of the folding to such a position as to bringthe blade to the predetermined level w-hen folding has been effected. lnadjusting the angle of the hinge axis the operator proceeds as follows:

(l) He manually disengages the tooth S8 of the pitch lock mechanism sothat this tooth will not interfere with fthe adjustments that must bemade.

(2) By means of the bail 166 or otherwise he then rotates the innersupporting element 36 and the outer portion of the blade so that thehinge axis Ais at the angle that is necessary for folding the blade atthe required level. When the inner supporting element is so rotated theretaining device 128 remains engaged so that there can be no pivotalmovement of the lifting portion about the hinge axis. The rotation iseffected in opposition to the resistance offered by the tension-torsionmembers 4Z, 42, but no substantial resistance is offered by the linkagefor moving the ap 28.

(3) Having rotated the inner supporting element 36 to place the hingeaxis at the required angle, he next moves the bail from the positionshown in FlGS. 2, 3 and 4 to the position shown in FIG. 12, the bailbeing then engaged and held by the latch 258. In moving the bail to theposition shown in FIG. 12, the operator has withdrawn the retainingmember 128 so that the arms 112 and 13.4 are free to move as requiredfor folding and he has also, by means of the rods 186 and the springs194, moved the ring 175 to the position shown in IFiG. 13 wherein theteeth 176 on the ring are interengaged with the teeth 4174- on thetubular portion 30. These intermeshing teeth lock the hinge axis at theangle to which it has been manually adjusted. In this position, thesprings are compressed and they prevent any movement of the ring 170 inthe outward or disengaging direction. As previously explained, there isno intermediate position `wherein the blade is free to move prematurelyabout its hinge axis.

(4) Having positioned the folding axis at the proper angie and havingreleased the outboard pontion of the blade for hinging or foldingmovement, he then swings it in the proper direction to the selectedfolded position. When there are four equally spaced blades as shown, theangles `of the hinge axes are such that the lifting structures ofadjacent blades are in superposed relationship. More specifically statedthe lifting structures of the blades A and B are in superposedrelationship and the lifting structures of the blades C and D are insuperposed relationship.

The invention claimed is:

l. A helicopter rotor having a hub and a plurality of generally radialblades, each comprising in combinationz' an inboard member connectedwith the hub,

an outboard lifting structure,

inner and outer supporting elements for said lifting structure, saidinner element being connected with the inboard member for relativerotative movement about a radial axis and said outer element beingiixedly connected with the lifting structure and being connected withthe inner element for pivotal folding movement about a normally verticalhinge axis,

an arm fixedly connected with the outer supporting element and extendinginwardly substantially beyond said pivotal axis which arm at its innerend has two transversely spaced prongs having inwardly diverging faces,

a retaining device comprising two separate parts each guided on saidinner supporting element movable relatively thereto into and out of anoperative position wherein it is in engagement with saidA arm and meansfor moving the two said parts of the retaining device in unison alongsaid inner supporting element and into and out of said operativeposition of said device which means is sutiiciently flexible to permitslight movement of said parts towards and from each other, said twoparts of the retaining device having inwardly diverging facesrespectively engageable with the inwardly diverging faces of the prongson said arm when said retaining device is in its said operative positionwhich said diverging faces when engaged with each other serve to movethe two parts of the retaining device toward each other and into firmengagement with said inner supporting member and also when so engagedserve to prevent lost motion between the retaining device and the arms.

2. A helicopter rotor having a hub and a plurality of generally radialblades, each comprising in combination:

an inboard member connected with the hub,

an outboard lifting structure,

inner and outer supporting elements for said lifting structure, saidinner element being connected with the inboard member for relativerotative movement about a radial axis and said outer element beingtixedly connected with the lifting structure and being connected withthe inner element for pivotal folding movement about a normallyvertically hinge axis,

an arm fixedly connected with the outer supporting element and extendinginwardly substantially beyond said pivotal axis which arm at its innerend has two oppositely disposed inclined faces which are exposed towardthe hub,

a retaining device guided on the inner supporting element forrectilinear radial movement into and out of an operative position whichretaining device is constructed and arranged to provide two oppositelydisposed inclined faces respectively engageable with said inclined faceson the arm to prevent pivotal folding movement when said device is inits operative position and to permit said pivotal folding movement whensaid device is out of its operative position,

a manually operable lever connected with the inner supporting elementfor movement about an axis perpendicular to said radial axis, and

a generally radial link which is pivotally connected at its respectiveends with said lever and with said retaining device so that the leverupon pivotal movement serves to move the retaining device either into orout of engagement with the arm, the pivotal axis of the lever and theaxes of pivotal connection of the link being so related that anovercenter toggle action is provided when the lever moves the retainingdevice into engagement with the arm.

3. A helicopter rotor as set forth in claim 2,

wherein said arm at its inner end has two transversely spaced prongs,

wherein said inclined faces are on said prongs and face toward eachother, and

wherein said inclined faces on the retaining device face away from eachother and are adapted to engage said inclined faces on the prongs.

4. A helicopter rotor having a hub and a plurality of generally radialblades, each comprising in combination:

an inboard member connected With the hub,

an outboard lifting structure,

inner and outer supporting elements for said lifting structure, saidinner element being connected with the inboard member for relativerotative movement about a radial axis and said outer element being xedlyconnected with the lifting structure and being connected with the innerelement for holding movement about a normally vertical pivotal hingeaxis,

two superposed arms iixedly connected with the outer supporting elementat the top and bottom thereof and extending inwardly substantiallybeyond said pivotal axis which superposed arms are respectively l2relatively to the inner supporting element which device is adapted inanother position to permit such pivotal folding movement, and

manually operable means when the rotor is idle for above and below theinner supporting element, and 5 retaining the inner supporting elementand the hinge a retaining device carried by said inner supportingeleaxis in any one of a plurality of rotatively different ment andradially movable relatively thereto which positions to which :they mayhave been moved, said retaining device has two super-posed portions thatretaining means serving to hold the hinge axis at a respectively moveinto or out of engagement with corresponding one of a plurality ofangles with resaid superposed arms, said device when in engagespect tothe inboard member and with respect to a ment with the arms preventingpivotal folding moveradial plane through the rotor axis with the resultment of the outer supporting element and the lifting that folding of theoutboard lifting structure may be structure about said hinge axis andrelatively to eected at a selected one of a plurality of levels. saidinner supporting element and said device when 8. A helicopter rotorhaving a hub and a plurality of out of engagement with the armspermitting such generally radial blades, each comprising in combination:pivotal folding movement. an inboard member connected "ith the hub andhaving f 5. A helicopter rotor as set forth in claim 4, a radial outertubular portion,

wherein a manually operable bail is connected with an outboard liftingstructure, f

the inner supporting element at opposite sides therean inner supportingelement having a radial inner tubu- Y of for movement about an axisperpendicular to 2o lell'eltol Wbeb SUYTOUUS he tubular P'OIOU ofthesaid radial axis, and mbeefl member, y

wherein two oppositely disposed generally radial links bearingslntepeeed between said tubular portions to are provided each of which ispivotally connectedV at faellltate relative rotative movement ci saidinner its respective ends with said bail and with said re- Supportingmember and 0f Peris baffled thereby taining device so that the bail uponpivotal moveabout e edleleXlS, ment serves to move the retaining deviceeither into an buffer Sllbpemg elem-eilt XediY C Olleted With the or outof engagement with the arms, the pivotal axis hflllg SfllCUe ebdf'JODEeCed .Wlth 'the inner SUP- of the bail and the axes of pivotalconnection of the P01" ting elemell't for 1 51V0l31-f0d1ng IHOVemeDtabout link being so related that an overcenter toggle action e nc'meuyVelleal binge 2}X1S, is provided when the bail 'moves the retainingdevice 30 a felellVeiY HlOVebe Tealbmg de VlCe adapted 1D One intoengagement with Said armsposition to prevent pivotal folding movement.of the 6. A helicopter rotor having a hub and four equally hftmgSlU-eure eltlVeiY i0 tbe limer SUPPOfbllg ele' spaced generally radialblades, each comprising in commeltWbleb d eVlee 1S etlepied m anotherPOSIUOH l0 bmation: permit such pivotal folding movement,

an inboard member Connected with the hub, a retaining ring connectedwith the tubular portion of the inner supporting element at the innerend thereof an outboardilitinff structure 1 a which ring is movableinwardly and outwardly relailnner and outer supporting elements for saidlifting structure, said inner element being connected with the inboardmember and said outer element being tively to the last said tubularportion but is held against rotation relatively thereto, and

ixedly connected with the lifting structure and being 4G two Selles 0ftee/lb IeSPeClVelY 0D Sald fing and 011 connected with the inner elementfor pivotal folding Bald lboed member Which teeth are interengageablemovement about a normally vertical hinge axis which upon mWeIdmbvemelbof Seid fing S0 that tbeX Pfeis angularly adjustable relativelyto said inboard mem- Vent 2111.5 Teltlve rotativeL movement of saidinner ber and relatively to a radial plane through the rotor sujppofmgelement and 0L tbe lafs ea{led 'thereby axis and Which axis is soadjustable independently Wlth me feebllhet S21-1d 'hlnge axis is held ata of the hinge axis for each other blade, 4D selected angle with respectto a radial plane through relatively movable retaining device adapted inone the mier axle position to prevent pivotal folding movement of -the9' A behcopef feter eS Set .fOrth `111 `Claim 8,

lifting structure relatively to the inner supporting ele- Wherfm there15 @0l/1de@ e lllg elllelufe that Includes l,

ment which device is adapted in another position to 0 Sad fetal-1mg fmgWhleh H113 Structure has an eX- permit such pivotal folding movement,and a Posd notch@ ih@ ?eflpbe'y 'fbefebfV 'find F manually operablemeans for retaining said hinge axis wherein there 1S Pfeilded a lOeklngdevice on the in- *i at any one `of a plurality of angles to which itmay board member hel/111g e eOh Winch 1S adapted t0 t have been adjustedrelatively to said inboard menienfer SEK? mmm and. 1S mellelly' movableOut 0f ber and relatively to said radial plane, said retaining saidnoten Said loekllg deVlCe belng automatically means being operableindependently of that or" ana0 @rable lo mol/e Sad teeth Into Said notchwhen other blade so that folding of the Outboard lifting the rotor isstationary or rotating at aspeed below structure may be eected at aselected one of a plua Prfdetermmed Speed S0 as the leek Seid lllel'Sb?- rality of levels and in parallel superposcd relatioupgftmgelementagamt elaflve 'aiming mevemelt ship with the lifting structure ofanother blade. and ,Sad locking device bemg COIlSl'uCed t0 Hetcentiiifugally to move said tooth out of said notch 7. A helicopterrotor having a hub and a plurality of generally radial blades, eachcomprising in combination:

an Iiriboard member connected with the hub,

an outboard lifting structure,

inner and outer supporting elements for said lifting structure, saidinner element being connected with the inboard member for rotativemovement relatively thereto about a radial axis and said outer elementbeing fixedly connected with the lifting structure and being connectedwith the inner element for pivotal folding movement about a normallyvertical hinge axis,

a relatively movable retaining device adapted in one position ltoprevent pivotal foldirny movement of the outer supporting element andthe lifting structure when the rotor is rotating at or above saidprede-termined speed and to thereby release said inner supportingelement to permit relative turning movenient thereof. 65 l0. Ahelicopter rotor having a hub and a plurality of generally radialblades, each comprising in combination:

an inboard member connected with the hub, an youtboard liftingstructure, inner and outer supporting elements for said liftingVstructure, said inner element being connected with the inboard memberfor rotative movement relatively thereto about a radial axis and saidouter element being iixedly connected with the lifting structure andbeing connected with the inner element for folding movement about anormally vertical pivotal axis,

a first retaining device movable into and out of an operative positionat which it prevents pivotal folding movement of the 'outer supportingelement and the lifting structure relatively to the inner supportingelement,

a second retaining device movable inwardly and outwardly into and out ofan operative position for retaining the inner supporting element in anyone of a plurality lof rotatively different positions to which it mayhave been moved, said retaining means serving to hold the hinge axis ata corresponding one of a plurality of angles with respect to the inboardmember and with respect to a radial plane through the rotor axis withthe result that folding of the outboard lifting structure may beeffected at a selected one of a plurality of levels,

a manually operable lever pivotally connected with the inner supportingelement,

a link connecting the lever with the last said retaining device forenabling the lever to move the last said device into and out of its saidoperative position, and a latch on the inner supporting member .forholding the lever in a position corresponding to said operative positionof the last said retaining device.

ll. A helicopter rotorY as set forth in claim 10,

wherein a compressible spring is interposed between said link and saidsecond retaining device which spring is compressed to hold the device inits said operative position when the lever is held by the latch.

l2. A helicopter rotor as set forth in claim 1G,

wherein said manually operable lever is connected with the innersupporting element for movement about an axis perpendicular to saidradial axis, and

wherein a generally radial link is provided which is pivotally connectedat its respective ends with said lever and with said second retainingdevice so that the lever upon pivotal movement thereof serves to movethe last said retaining device either into or out of its said operativeposition, the pivotal axis of the lever and the axes of pivotalconnection of the link are so related that an overcenter toggle actionis provided when the lever moves said second retaining device out of itssaid operative position.

13. A helicopter rotor having a hub and a plurality of generally radialblades, each comprising in combination:

an inboard member connected with the hub,

an outboard lifting structure,

inner and outer supporting elements for said liilting structure, saidinner element being connected with the inboard member and said outerelement being fixedly connected with the lifting structure,

mechanism operable during rotor rotation for changing the pitch of saidlifting structure,

hinge means connecting said outer supporting element and the liftingstructure with said inner supporting element for pivotal foldingmovement about a normally vertical hinge axis,

means connecting said inner supporting element with said inboard memberfor rotative movement of said inner supporting element and of said hingemeans relatively to the inboard member independently of the action ofsaid pitch changing mechanism,

a first retaining device movable into and out of an operative positionat which it prevents pivotal folding movement of the outer supportingelement and the lifting structure relatively to the inner supportingelement,

a second retaining device movable into and out of an operative positionat which it retains said inner supporting element with the axis of thehinge means at any one of a plurality of angles with respect to theinboard member and with respect to a radial plane through the rotor axiswith the result that folding of the outboard lifting struc-ture may beeffected at a selected one of a plurality of levels, and

id a single means movable in one direction [for simultaneously movingsaid rst and second retaining devices out of and into their respectiveoperative positions and serving upon lever movement in the reversedirec-tion to move said first and second retaining devicessimultaneously into or out of their respective operative positions.

14. A helicopter rotor as set forth in claim 13,

wherein the last said means is constructed and arranged to move saidsecond retaining device sufficiently -to `be effective before said firstretaining device has been moved sufficiently to be ineffective.

15. A helicopter rotor as set forth in claim 14,

wherein rst retaining device is movable radially outwardly to itsoperative position, and

wherein said second retaining device is movable radially inwardly to itsoperative position.

16. A helicopter rotor as set forth in claim 13,

wherein the last said means includes a manually operable lever movablein opposite directions with respect to the inner supporting element andalso includes elements connected with said lever and serving upon levermovement in one direction to simultaneously move said first and secondretaining devices out of and into their respective operative positionsand serving upon lever movement in the reverse direction to move saidfirst and second retaining devices simultaneously into or out of theirrespective operative positions.

17. A helicopter rotor as set forth in claim 16,

wherein said first and second retaining devices are connected with eachother for radial movement in unison,

wherein said lever is connected with the inner supporting element formovement about an axis perpendicular to said radial axis, and

wherein a generally radial link is provided which is pivotally connectedat its respective ends with said lever and with said retaining devicesso that the lever upon pivotal movement serves to move the retainingdevices radially inwardly or radially outwardly, the pivotal axis of thelever and the axes of pivotal connection of the link being so relatedthat an overcenter toggle action is provided when the lever moves theretaining devices radially outwardly to move the first retaining deviceinto its operative position and to move the second retaining device outof its operative position.

18. A helicopter rotor as set forth in claim 17,

wherein a latch is provided which is adapted 'to hold said lever in theposition corresponding to the inopertive position of the first retainingdevice and the operative position of the second retaining device.

19. A helicopter rotor as set .fforth in claim 16,

wherein said first and second retaining devices are connected with eachother for radial movement in unison,

wherein said lever is connected with the inner supporting element formovement about an axis perpendicular to said radial axis,

wherein a generally radial link is provided which is pivotally connecteda-t its respective ends with said lever and with said retaining devicesso that the lever upon pivotal movement serves to move the retainingdevices radially inwardly or radially outwardly,

wherein compressible springs are superposed between said retainingdevices,

wherein means is provided for limiting inward movement of said secondretaining device beyond its operative position with the result that saidsprings are compressed when the first retaining device is Inoved toitsinoperative position, and

wherein a latch is provided which is adapted lto hold said lever in theposition corresponding to the inoperative position of the firstretaining device and the operative position of the second retainingdevice.

20. A helicopter rotor having a hub and a plurality of 15 generallyradial blades, each comprising in combination:

an inboard member connected with the hub,

an outboard lifting structure,

inner and outer supporting elements for said lifting structure, saidinner element being connected with the inboard member and said outerelement being fixedly connected With the lifting structure and beingconnected With the inner element for pivotal folding movement about anormally vertical hinge axis,

a relatively movable retaining device adapted in one position to preventpivotal folding movement of the outer supporting element and the liftingstructure relatively to Ithe inner supporting element which device isadapted in another position to permit such pivotal folding movement,

mechanism operable durinfy rotor rotation for changing the pitch of saidlifting structure,

hinge means connecting said outer supporting element and the liftingstructure With said inner supporting element for pivotal foldingmovement about a normally vertical hinge axis,

means connecting said inner supporting element With said inboard memberfor rotative movement of said inner supporting element and `of sm'dhinge means relatively to the inboard member independently of the actionof said pitch changing mechanism, and

manually operable means when the rotor is idle for retaining the innersupporting element and the hinge axis in any one of a plurality ofrotatively dierent positions to Which they may have been moved, saidretaining means serving to hold the hinge axis at a corresponding one ofa plurality of angles With respect to the inboard member and withrespect to a radial plane through the rotor axis with the result thatfolding of the outboard lifting structure may be effected at a selectedone of a plurality of levels.

21. A helicopter rotor as set forth in claim 20,

wherein the mechanism for changing the fpitch of said lifting structureincludes an aerodynamic servo-flap carried by said lifting structuretogether with ap controlling means extending along the blade from thehub to the flap which flap has no pitch changing eifeot when the rotoris idle and therefore leaves the inner supporting member and the hingemeans free to be rotatively adjusted relatively to the inboard member.

22. A helicopter rotor as set forth in claim 20,

wherein said rotor has four equally spaced blades, and

wherein the inner supporting member and the hinge device of each bladeare rotatively movable independently of those of each other blade sothat folding lof the lifting structure of each blade may be effected ata selected level and in parallel superposed relationship with thelifting structure of another blade.

References Cited in the file of this patent UNITED STATES PATENTS1,144,471 Gustafson et al June 29, 1915 1,291,237 Sturrock Jan. 14, 19191,989,544 Campbell Jan. 20, 1935 2,029,484 Howard et al. Feb. 4, 19362,467,579 Boudreau Apr. 19, 1949 2,497,040 Williams Feb. 7, 19502,658,576 Mosinskis Nov. l0 1953 2,812,961 Brown et al Nov. 12, 19572,815,820 Papadakos Dec. 10, 1957 2,966,947 Batesole Jan. 3, 1961FOREIGN PATENTS 668,895 Germany Dec. 12, 1938

6. A HELICOPTER ROTOR HAVING A HUB AND FOUR EQUALLY SPACED GENERALLYRADIAL BLADES, EACH COMPRISING IN COMBINATION: AN INBOARD MEMBERCONNECTED WITH THE HUB, AN OUTBOARD LIFTING STRUCTURE, INNER AND OUTERSUPPORTING ELEMENTS FOR SAID LIFTING STRUCTURE, SAID INNER ELEMENT BEINGCONNECTED WITH THE INBOARD MEMBER AND SAID OUTER ELEMENT BEING FIXEDLYCONNECTED WITH THE LIFTING STRUCTURE AND BEING CONNECTED WITH THE INNERELEMENT FOR PIVOTAL FOLDING MOVEMENT ABOUT A NORMALLY VERTICAL HINGEAXIS WHICH IS ANGULARLY ADJUSTABLE RELATIVELY TO SAID INBOARD MEMBER ANDRELATIVELY TO A RADIAL PLANE THROUGH THE ROTOR AXIS AND WHICH AXIS IS SOADJUSTABLE INDEPENDENTLY OF THE HINGE AXIS FOR EACH OTHER BLADE, ARELATIVELY MOVABLE RETAINING DEVICE ADAPTED IN ONE POSITION TO PREVENTPIVOTAL FOLDING MOVEMENT OF THE LIFTING STRUCTURE RELATIVELY TO THEINNER SUPPORTING ELEMENT WHICH DEVICE IS ADAPTED IN ANOTHER POSITION TOPERMIT SUCH PIVOTAL FOLDING MOVEMENT, AND MANUALLY OPERABLE MEANS FORRETAINING SAID HINGE AXIS AT ANY ONE OF A PLURALITY OF ANGLES TO WHICHIT MAY HAVE BEEN ADJUSTED RELATIVELY TO SAID INBOARD MEMBER ANDRELATIVELY TO SAID RADIAL PLANE, SAID RETAINING MEANS BEING OPERABLEINDEPENDENTLY OF THAT OF ANOTHER BLADE SO THAT FOLDING OF THE OUTBOARDLIFTING STRUCTURE MAY BE EFFECTED AT A SELECTED ONE OF A PLURALITY OFLEVELS AND IN PARALLEL SUPERPOSED RELATIONSHIP WITH THE LIFTINGSTRUCTURE OF ANOTHER BLADE.